This invention relates to a silver halide emulsion and a photographic silver halide light-sensitive material using the same. More particularly, it relates to a novel and improved photographic silver halide light-sensitive material having improved shelf stability and high sensitivity.
In general, silver halides used in photographic silver halide light-sensitive materials are chemically sensitized in order to obtain the desired sensitivity and gradation. Many sensitizing methods are known in the art, including sulfur sensitization using sulfur-containing compounds or active gelatin capable of reacting with silver ions, reduction sensitization using reducing materials, and noble metal sensitization using gold and similar noble metals. These methods may be used alone or in combination. Sulfur sensitizers include thiosulfates, thioureas, thiazoles, rhodanines and other compounds, with illustrative examples being described in U.S. Pat. Nos. 1,574,944; 2,410,689; 2,278,947; 2,728,668; 3,656,955; 4,030,928; and 4,067,740. Reducing sensitizers include stannous salts, amine salts, hydrazine derivatives, formamidine sulfinic acid, silane compounds and other compounds, with illustrative examples being described in U.S. Pat. Nos. 2,487,850; 2,419,974; 2,518,698; 2,983,609; 2,983,610; 2,694,637; 3,930,867; and 4,054,458. For noble metal sensitization, complex salts of metals belonging to Group VIII of the Periodic Table, such as platinum, iridium, and palladium may be used. Illustrative examples are described in U.S. Pat. Nos. 2,399,083 and 2,448,060; and British Patent No. 618,061.
There is an increasing need for silver halide emulsions with higher sensitivity. For such a purpose, it is essential to use more than one of the above-described chemical sensitization methods in combination, most often a combined method using sulfur and noble metal sensitizers, especially a combined gold-sulfur sensitization method using sulfur and gold sensitizers.
In such combined sensitization, the amounts of the sensitizers used depend on the state of silver halide grains (such as grain size and its distribution, halogen composition, and crystal habit), the environmental parameters (such as the amount and type of binder, pH, pAg, reaction temperature, and reaction time), and auxiliary agents for gold sensitization (such as promoters, typically thiocyanates and thioether compounds, and antifoggants, typically thiosulfonates) as well as the type of particular sulfur and gold sensitizers used. Determination of sensitizer amounts and the procedure of carrying out combined sensitization are well known to those skilled in the art.
These chemical sensitizers, when added to a silver halide emulsion, do not have reacted to the entirety of their amounts added, and part of them remains unreacted in the silver halide emulsion. Such a silver halide emulsion often undergoes a change during preparation or storage of a light-sensitive material, incurring a change with time in the photographic properties. This adverse effect is considered due to the presence of residual chemical sensitizers in the binder phase of the silver halide emulsion. Particularly the gold sensitizer which remains in the binder phase in a substantial amount is liable to migrate into the silver halide grain phase through diffusion or the like with time during the period from chemical sensitization to application to a support, or even after the application, incurring an undesirable change with time in photographic properties including sensitivity, gradation and fog.
To suppress such a phenomenon, efforts have been made to reduce the amount of gold sensitizer left in the binder phase by changing the chemical sensitizing conditions or using a palladium complex salt in combination. These methods are still insufficient. The prior art technique has the limit that the maximum amount of gold which can be contained in the silver halide phase is about 70% of the entire amount of gold added as demonstrated in the Example given later wherein the amounts of gold contained in the silver halide and binder (gelatin) phases are measured.
The adverse effect of remaining chemical sensitizers on photographic properties as mentioned above is outstanding when the silver halide emulsion used is of surface latent image type. There is a need for improving the age stability of a silver halide emulsion of surface latent image type by minimizing the amount of gold sensitizer remaining in the binder phase.